The background of the present invention is described herein in the context of subscription television systems, such as cable television and direct broadcast satellite (DBS) systems, that distribute a variety of program services to subscribers, but the invention is by no means limited thereto except as expressly set forth in the accompanying claims.
In the subscription television industry, "programmers" produce "programs" for distribution to various remote locations. A "program" is a collection of related video, audio and other services, such as closed-captioning and teletext services. A single programmer may wish to supply many such programs. Typically, a programmer will supply these services via satellite to either individual subscribers (e.g., DBS subscribers), cable television operators, or both. In the case of cable television operators, the services transmitted via satellite are received at the operator's "cable head-end" installations. A cable operator typically receives programs and other services from many programmers and then distributes them to its subscribers. In addition, a cable operator may insert locally produced services at the cable-head end. The selected services and locally produced services are then transmitted to the individual subscribers via a coaxial cable distribution network. In the case of DBS subscribers, each subscriber is capable of receiving a satellite down-link from the programmers directly.
In the past, subscription television systems, including cable and DBS systems, have operated in the analog domain. Recently, however, the subscription television industry has begun to move toward all digital or hybrid analog/digital systems wherein prior to transmission, all or some of the analog signals are converted to digital signals. Digital signal transmission offers the advantage that digital data can be processed at both the transmission and reception ends to improve picture quality. In addition, digital data compression techniques have been developed that achieve high signal compression ratios. Digital compression allows a larger number of individual services to be transmitted within a fixed bandwidth. Bandwidth limitations are imposed by both satellite transponders and coaxial cable distribution networks, and therefore, digital compression is extremely advantageous.
In some prior art digital service transmission systems, various digital services, such as video services and audio services, are multiplexed into a single multiplex data stream for transmission to subscribers and cable operators. Unfortunately, these prior art systems are inflexible in many respects and cannot be easily adapted to meet the continuously changing requirements of the industry. There is a need, therefore, for a system and method of multiplexing a plurality of digital services that provides a high degree of flexibility so that the system can easily be adapted to meet the diverse and ever changing demands of the industry. In particular, such a system should be capable of multiplexing a wide variety of digital services. As those skilled in the art know, digital services vary widely in individual data rates. For example, digital audio service rates differ substantially from digital video service rates. A digital services delivery system must therefore be flexible in service data rate allocation within the system. Also, such a system should have an overall data transmission rate that is "scalable," i.e., that is adjustable over an almost continuous range. As those skilled in the art can appreciate, digital service delivery may take place via satellite, cable distribution networks, or even optical fiber networks. Each of these mediums has a unique bandwidth limitation, and therefore, accommodates a different maximum data rate. It is desirable, therefore, that a digital services delivery system provide adjustability (i.e., scalability) in the overall data transmission rate of the system.
In addition to service rate flexibility and overall data transmission rate scalability, a program services delivery system should provide for easy and cost efficient demultiplexing and re-multiplexing of the individual services being transmitted. Cable operators typically receive "programming" (i.e., related digital services) from a multitude of "programmers." Cable operators rarely provide their subscribers with every service provided by every programmer; more typically, cable operators select various services from each programmer and then provide only those selected services to their subscribers. Consequently, there is a need for a digital services delivery system and method that provides easy and cost-efficient de-multiplexing and re-multiplexing of various services. Regional hub distribution techniques will further emphasize this need.
As described hereinafter, the system and method of the present invention achieves each of the aforementioned objectives.